Revista Chilena de Historia Natural 75 (1): 105-116, 2002
Generalizations in the interactions between plants and pollinators
A controversy exists about the importance of generalization versus specialization in
pollination systems. Whereas the evolutionary and ecological theory speculates that the plant-pollinator systems should be highly
specialized, many evolutionary ecologists now acknowledge that generalization is frequent in natural systems. There is still no
consensus about which ecological factors can promote this counter-intuitive and paradoxical result. I propose that generalization in
plant-pollination systems can arise by several non-exclusive factors. One kind of factors are related to the ability of pollinators of acting
as true selective agents. Despite that many studies have shown that pollinators can provoke phenotypic selection on floral traits, only
occasionally it has been shown that this selection actually produces any response to selection. Two main reasons can explain why
pollinators cannot induce adaptations in many plants: (1a) a significant spatial and temporal variability in pollinator abundance and
identity highly reduces the possibilities of congruent selection on floral traits; (1b) the occurrence of extrinsic factors acting during
another stages of the plant reproductive and recruitment processes can also decrease the actual effect that pollinators has on fitness.
A second group of factors are those related with the fact that, to specialization occurs, it is necessary that two different pollinators can
constitute as completely separated selective agents, by differing in their per-visit efficiencies and/or floral trait preferences. By contrast,
similarity in efficiency and preference will constrain specialization even although pollinators act as selective pressures, since plant will
have not any criteria to benefit a given pollinator species with respect to the other.
Key words:
generalization,
specialization, pollination biology, evolutionary ecology, plant-pollinator interactions
